1. Field of the Invention
The present invention relates generally to optical devices and, more specifically, the present invention relates to dispersion compensation devices.
2. Background Information
The need for fast and efficient optical-based technologies is increasing as the growth rate of Internet data traffic overtakes that of voice traffic, pushing the need for fiber optic communications. Transmission of multiple optical channels over the same fiber in a dense wavelength-division multiplexing (DWDM) system provides a simple way to use the unprecedented capacity (signal bandwidth) offered by fiber optics. Commonly used optical components in the system include wavelength-division multiplexing (WDM) transmitters and receivers, optical add/drop multiplexers, optical filters such as diffraction gratings, thin-film filters, fiber Bragg gratings, and arrayed-waveguide gratings.
It is well known that high-speed baseband optical signals are degraded when transmitted over single-mode fibers due to multiple effects such as chromatic dispersion and polarization mode dispersion. In order to extend the transmission distance of these signals, particularly in dynamically reconfigurable WDM systems, tunable dispersion compensation devices are utilized. Known tunable dispersion compensation devices are dispersion compensation fibers, which provide wavelength tuning, for example, by mechanically stretching nonlinearly chirped fiber Bragg gratings.
A fiber Bragg grating is an optical fiber device typically made of silica that is constructed by creating periodic changes in the refractive index of fiber core materials along the fiber length. These index changes may be formed by exposing the photosensitive core to intense optical interference patterns. With a nonlinearly chirped fiber Bragg grating, the fiber Bragg grating has a periodicity that varies nonlinearly along the length of the fiber and therefore produces a relative group delay that varies nonlinearly with the wavelength of light.
With nonlinearly chirped fiber Bragg grating, there is no dispersion tuning since at any particular wavelength of light, the grating-induced dispersion is substantially fixed. Nominal adjustments are made by physically or mechanically stretching the fiber with external mechanical stretchers such as piezoelectric transducers to modify the periodicity of the nonlinearly chirped fiber Bragg grating. A disadvantage with this technique is that the tuning range of the nonlinearly chirped fiber Bragg grating is relatively small and the fiber may suffer damage from the stress and strain induced by the physical stretching. In addition, high voltages in the order of ˜1000 volts are necessary in order to operate piezoelectric transducers to physically stretch the fiber Bragg gratings. Another limitation with known dispersion compensation fibers is that insertion losses resulting from attenuation and/or coupling are generally very high. Consequently, optical power and budgets are adversely effected with the use of known dispersion compensation devices.